JP2004191599A - Zoom lens and electronic still camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has a high resolution, a short optical entire length in no-use, corrects a distortion favorably, and shows a low sensitivity. <P>SOLUTION: The zoom lens is provided with a first lens group 10 of negative power, a second lens group 20 of positive power, and a third lens group 30 of positive power from an object side. When the distance from the top of an object side to an image face in a wide angle end is L<SB>W</SB>, the distance from the top of the object side to an image face in a telescopic end is L<SB>T</SB>, the focal distance of the whole lens system in the wide angle end in infinity of a photographing distance is f<SB>W</SB>, the focal distance of the second lens group 20 is f<SB>G2</SB>, the focal distance of the third lens group 30 is f<SB>G3</SB>, the focal distance of a fourth lens from the object side is f<SB>4</SB>, and the focal distance of an eighth lens from the object side is f<SB>8</SB>, the relation of ¾L<SB>W</SB>-L<SB>T</SB>¾/L<SB>W</SB><0.1, 2.5<f<SB>G2</SB>/f<SB>W</SB><3, 5<f<SB>G3</SB>/f<SB>W</SB><6, 1.4<f<SB>4</SB>/f<SB>G2</SB><1.6, and 0.5<f<SB>8</SB>/f<SB>G2</SB><0.7 is satisfied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００７８】
ここで、κは円錐定数、ｒは非球面頂点の曲率半径、Ｄ、Ｅ、Ｆ、Ｇはそれぞれ４次、６次、８次、１０次の非球面係数、ｈは光軸からの高さ、Ｚは非球面上の光軸からの高さがｈの点におけるサグ量である。
【００７９】
非球面の光軸からの高さがｈの点における局所曲率半径ρは、以下の（数２）により与えられる。
【００８０】
【数２】

【００８１】
撮影距離が無限遠の場合の広角端の焦点距離をｆ_Ｗ、望遠端の焦点距離をｆ_Ｔとすると、以下の（数３）の焦点距離ｆ_Ｎとなるズーム位置を中間位置と呼ぶことにする。
【００８２】
【数３】

【００８３】
ズームレンズのレンズデータを以下の表１に示す。
【００８４】
【表１】

【００８５】
非球面データを以下の表２に示す。
【００８６】
【表２】

【００８７】
撮影距離が無限遠の場合の可変面間隔データを以下の表３に示す。
【００８８】
【表３】

【００８９】
なお、表中の長さの単位はすべてｍｍである。ｒは曲率半径、ｄは面間隔、ｎｄ、νｄはそれぞれｄ線における屈折率、アッベ数である。Ｇ１〜Ｇ３は第１〜第３レンズ群に対応しており、Ｌ１〜Ｌ９は第１〜第９レンズに対応しており、Ｐは平行平板素子４０に対応している。＊印を付した面は非球面である。また、表３において、ｄ６、ｄ１７、ｄ１９は可変部の面間隔であり、図１にその位置を示しており、ｆは焦点距離、ＦはＦナンバー、ω（°）は入射半画角、Ｌは光学全長を示している。これらの表に関する説明は、以下の各表においても同様である。
【００９０】
実施例１に係るズームレンズの撮影距離が無限遠で絞り開放時の収差図を、図２〜図４に示している。図２は広角端の場合、図３は中間位置の場合、図４は望遠端の場合である。各図における（ａ）図は球面収差（ｍｍ）、（ｂ）図は非点収差（ｍｍ）、（ｃ）図は歪曲収差（％）をそれぞれ示している。
【００９１】
また、球面収差図において、実線はｄ線、短破線はＦ線、長破線はＣ線の特性である。非点収差図において、実線はサジタル平面、破線はメリディオナル平面の特性である。図２〜図４より、ズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【００９２】
実施例１では、固体撮像素子として、有効画素数が水平２０４８×垂直１５３６、画素ピッチが水平２．８μｍ×垂直２．８μｍ、実効画面サイズが水平５．７３４４ｍｍ×垂直４．３００８ｍｍのものを用いることができる。また、固体撮像素子として、実効開口率の向上のために画素ごとにマイクロレンズを設けたものを用いることができる。このことは、以下の実施例２〜５についても同様である。
【００９３】
図１に示したズームレンズは、第２レンズ群の偏心敏感度が高い。このため、図１の構成では、第５レンズ５と第６レンズ６とを接合し、第７レンズ７と第８レンズ８とを接合させている。また、第４レンズ４は像側面を凹面として、必要であれば組み立て時に第４レンズ４を調心しやすいようにしている。
【００９４】
第５レンズ５と第６レンズ６、第７レンズ７と第８レンズ８とを接合すると、接着剤の両面の境界では屈折率差が小さくなるため、偏心敏感度は低くなる。また、接合した場合は、面間隔誤差を発生しやすいスペーサが不要であるため、スペーサを用いる場合に比べて面間隔の誤差を小さくすることができる。
【００９５】
調心を行う場合は、次のようにするとよい。第５レンズ５と第６レンズ６とを接合したものと、第７レンズ７と第８レンズ８とを接合したものをレンズ枠に組み込んだ後に、第４レンズ４を所定の位置に取り付け、偏心測定装置を利用して第２レンズ群２０全体の偏心が小さくなるように、第４レンズ４の位置を調整し、最後に接着剤により第４レンズ４をレンズ枠に固定する。
【００９６】
このとき、第４レンズ４の像側面が凸面の場合には、第４レンズ４を移動させようとすると、平行偏心と傾斜偏心との両方を生じるため、調心が難しくなる。これに対して、前記のように、第４レンズ４の像側面を凹面（又は平面）としていれば、第４レンズ４を傾斜させることなく平行移動させることができるため、調心が容易になる。
【００９７】
また、固体撮像素子を１°以内で傾斜させることにより、固体撮像素子上の結像特性を良好にすることができる。
【００９８】
以上のように、実施例１に係るズームレンズは、ズーム比が３．０倍、広角端における画角が７６．５°程度で、解像度が高く、非使用時光学全長が短く、歪曲収差が良好に補正されたものとなっている。
【００９９】
なお、前記のレンズの接合、調心、及び固体撮像素子の傾斜に関する説明は、以下の実施例２〜５についても同様である。
【０１００】
（実施例２）
実施例２に係るズームレンズ基本構成は、実施例１と同様であるが、実施例２では一部のレンズの材質が異なっている。実施例２に係るズームレンズのレンズデータを以下の表４に示す。
【０１０１】
【表４】

【０１０２】
非球面データを以下の表５に示す。
【０１０３】
【表５】

【０１０４】
撮影距離が無限遠の場合の可変面間隔データを以下の表６に示す。
【０１０５】
【表６】

【０１０６】
実施例２に係るズームレンズの撮影距離が無限遠で絞り開放時の収差図を、図５〜図７に示している。図５〜図７より、ズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【０１０７】
本実施例においても、第４レンズの像面側を凹面としているので、必要であれば、実施例１と同様に、第４レンズの調心を容易に行うことができる。また、固体撮像素子を１°以内で傾斜させることにより、固体撮像素子上の結像特性を良好にすることができる。
【０１０８】
以上のように、実施例２に係るズームレンズは、ズーム比が３．０倍、広角端における画角が７６．５°程度で、解像度が高く、非使用時光学全長が短く、歪曲収差が良好に補正されたものとなっている。
【０１０９】
（実施例３）
実施例３に係るズームレンズ基本構成は、実施例１と同様であるが、実施例３では一部のレンズの材質が異なっている。実施例３に係るズームレンズのレンズデータを以下の表７に示す。
【０１１０】
【表７】

【０１１１】
非球面データを以下の表８に示す。
【０１１２】
【表８】

【０１１３】
撮影距離が無限遠の場合の可変面間隔データを以下の表９に示す。
【０１１４】
【表９】

【０１１５】
実施例３に係るズームレンズの撮影距離が無限遠で絞り開放時の収差図を、図８〜図１０に示している。図８〜図１０より、ズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【０１１６】
本実施例においても、第４レンズの像面側を凹面としているので、必要であれば、実施例１と同様に、第４レンズの調心を容易に行うことができる。また、固体撮像素子を１°以内で傾斜させることにより、固体撮像素子上の結像特性を良好にすることができる。
【０１１７】
以上のように、実施例３に係るズームレンズは、ズーム比が３．０倍、広角端における画角が７６．５°程度で、解像度が高く、非使用時光学全長が短く、歪曲収差が良好に補正されたものとなっている。
【０１１８】
（実施例４）
実施例４に係るズームレンズ基本構成は、実施例１と同様であるが、実施例４では一部のレンズの材質が異なっている。実施例４に係るズームレンズのレンズデータを以下の表１０に示す。
【０１１９】
【表１０】

【０１２０】
非球面データを以下の表１１に示す。
【０１２１】
【表１１】

【０１２２】
撮影距離が無限遠の場合の可変面間隔データを以下の表１２に示す。
【０１２３】
【表１２】

【０１２４】
実施例４に係るズームレンズの撮影距離が無限遠で絞り開放時の収差図を、図１１〜図１３に示している。図１１〜図１３より、ズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【０１２５】
本実施例においても、第４レンズの像面側を凹面としているので、必要であれば、実施例１と同様に、第４レンズの調心を容易に行うことができる。また、固体撮像素子を１°以内で傾斜させることにより、固体撮像素子上の結像特性を良好にすることができる。
【０１２６】
以上のように、実施例４に係るズームレンズは、ズーム比が３．０倍、広角端における画角が７６．５°程度で、解像度が高く、非使用時光学全長が短く、歪曲収差が良好に補正されたものとなっている。
【０１２７】
（実施例５）
実施例５に係るズームレンズ基本構成は、実施例１と同様であるが、実施例４では一部のレンズの材質が異なっている。実施例５に係るズームレンズのレンズデータを以下の表１３に示す。
【０１２８】
【表１３】

【０１２９】
非球面データを以下の表１４に示す。
【０１３０】
【表１４】

【０１３１】
撮影距離が無限遠の場合の可変面間隔データを以下の表１５に示す。
【０１３２】
【表１５】

【０１３３】
実施例５に係るズームレンズの撮影距離が無限遠で絞り開放時の収差図を、図１４〜図１６に示している。図１４〜図１６より、ズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【０１３４】
本実施例においても、第４レンズの像面側を凹面としているので、必要であれば、実施例１と同様に、第４レンズの調心を容易に行うことができる。また、固体撮像素子を１°以内で傾斜させることにより、固体撮像素子上の結像特性を良好にすることができる。
【０１３５】
以上のように、実施例５に係るズームレンズは、ズーム比が３．０倍、広角端における画角が７６．５°程度で、解像度が高く、非使用時光学全長が短く、歪曲収差が良好に補正されたものとなっている。
【０１３６】
前記実施例１〜５の前記条件式（１）〜（１５）の値を表１６に示す。表１６中、Ｅ−０４とあるのは、×１０^−４のことである。
【０１３７】
【表１６】

【０１３８】
（実施の形態２）
図１７は、本発明の実施の形態２に係る電子スチルカメラの概略構成図を示したものである。図１７において、６０はズームレンズ、５１は固体撮像素子、６１は液晶モニタ、１１は第１レンズ群、２２は絞り、２１は第２レンズ群、３１は第３レンズ群である。
【０１３９】
筐体６２の前側にズームレンズ６０が配置され、ズームレンズ６０の後側には、物体側から順に、光学ローパスフィルタ４１、固体撮像素子５１が配置されている。筐体６２の後側に液晶モニタ６１が配置され、固体撮像素子５１と液晶モニタ６１とは近接している。
【０１４０】
光学ローパスフィルタ４１は、物体側から順に、第１水晶板、第２水晶板、第３水晶板を透明接着剤により互いに接合したものである。３枚の水晶板は平行平面であり、各光学軸はいずれも光軸に対して４５°傾斜している。また、各水晶板の光学軸を固体撮像素子５１の撮像面５２に射影した方向は、ズームレンズ６０側から見て、第１水晶板については画面水平方向から左回りに４５°回転した方向、第２水晶板については画面水平方向から右回りに４５°回転した方向、第３水晶板については画面水平方向となっている。光学ローパスフィルタ４１は、固体撮像素子５１の画素構造に起因するモアレなどの誤信号の発生を防いでいる。光学ローパスフィルタ４１の物体側面には、赤外光を反射し、可視光を透過させる光学多層膜が蒸着されている。
【０１４１】
固体撮像素子５１は、有効画素数が水平２０４８×垂直１５３６、画素ピッチが水平２．８μｍ×垂直２．８μｍ、有効画面サイズが水平５．７３４４ｍｍ×垂直４．３００８ｍｍであり、各画素に微小正レンズが設けられている。固体撮像素子５１の物体側にはカバーガラス４２が設けられている。ズームレンズ６０による被写体の像が撮像面５２に形成される。
【０１４２】
ズームレンズ６０として、図１に示したズームレンズが用いられている。ズームレンズ６０は物体側から順に、第１レンズ群１１、絞り２２、第２レンズ群２１、第３レンズ群３１で構成されている。
【０１４３】
鏡筒は、移動鏡筒６３、第１の円筒カム６４、主鏡筒６５、第２の円筒カム６６、第２レンズ群枠６７、第３レンズ群枠６８で構成されている。第１レンズ群１１は移動鏡筒６３に取り付けられ、第２レンズ群２１と絞り２２とは第２レンズ群枠６７に取り付けられ、第３レンズ群３１は第３レンズ群枠６８に取り付けられている。第２の円筒カム６６を回転させると、第１の円筒カム６４が回転しながら光軸方向に移動し、第１の円筒カム６４が回転すると、移動鏡筒６３と第２レンズ群枠６７が移動するようになっている。こうして、第２の円筒カム６６を回転させると、第１レンズ群１１と第２レンズ群２１とが固体撮像素子５１を基準にした所定の位置に移動するので、広角端から望遠端までの変倍を行うことができる。
【０１４４】
第３レンズ群枠６８はフォーカス調整用モータにより光軸方向に移動可能である。モータにより第３レンズ群３１を光軸方向に移動させながら撮影画像の高周波成分がピークとなる位置を検出して、その位置に第３レンズ群３１を移動させれば、オートフォーカス調整を行うことができる。
【０１４５】
非使用時に第１レンズ群１１、第２レンズ群２１、第３レンズ群３１をすべて固体撮像素子５１側に寄せれば、沈胴式となり、ズームレンズの非使用時の光学全長を非常に短くすることができる。第１レンズ群１１と第２レンズ群２１とを固体撮像素子５１側に寄せるには、第１の円筒カム６４と第２の円筒カム６６のカム溝を伸ばすことにより可能となる。
【０１４６】
こうして、ズーム比が２．５〜３．２倍、広角端における画角が７０°〜８０°程度で、解像度が高く、非使用時の奥行が薄い電子スチルカメラを提供することができる。
【０１４７】
なお、図１７に示した電子スチルカメラのズームレンズには、前記実施例１〜５に示したいずれかのズームレンズを用いてもよい。
【０１４８】
また、図１７に示した電子スチルカメラの光学系は、動画を対象とするビデオカメラに用いることもできる。この場合、解像度の高い静止画だけでなく、動画も撮影することができる。
【０１４９】
（実施の形態３）
図１８は実施の形態３に係る電子スチルカメラの腰部構成図を示したものである。図１７と同一構成のものは同一番号を付して、その詳細な説明は省略する。図１８は、図１７に示したような電子スチルカメラにおいて、ズームレンズ６０に対して固体撮像素子５１を傾斜させて取り付けられるように変更した構成を示したものである。
【０１５０】
固体撮像素子５１は、取り付け板７０が取り付けられている。取り付け板７０には周辺部の３個所に穴が設けられ、主鏡筒６５には取り付け板７０の３個所の穴に対応する３個所にビス穴が設けられている。主鏡筒６５の３つのビス穴のうちの２つの近傍に２つの穴が設けられ、その２つの穴にはそれぞれバネ７２が挿入されている。取り付け板７０を主鏡筒６５に取り付け、３本のビス７１（１本のビスは図示せず）が、取り付け板７０の３つの穴を貫通して主鏡筒に取り付けられている。このとき、バネ７２が取り付け板７０を押すように作用するので、バネ７２の近傍のビス７１を回すことにより、固体撮像素子５１の傾斜角と傾斜方位を自由に変えることができる。調整完了後に３本のビスを接着剤で固定すれば、その後はズームレンズ６０に対する固体撮像素子５１の位置、姿勢を安定に保持することができる。
【０１５１】
このようにすると、ズームレンズ６０の各レンズ面が偏心している場合、固体撮像素子５１をその撮像面５２がズームレンズ６０の光軸と垂直となるように取り付けると、撮像面５２の一部の領域で結像特性が良くない場合があるが、固体撮像素子５１を適切に傾斜させることにより、撮像面５２に生じていた結像特性の良くない領域の結像特性を改善することができる。
【０１５２】
固体撮像素子５１の傾斜角範囲は１°程度にするとよい。固体撮像素子５１の傾斜調整は、実際に広角端から望遠端までのいくつかのズーム位置で撮影し、固体撮像素子５１からの出力信号から結像特性の良くない領域を探し、次に、出力信号を見ながら、２つのバネ７２の近傍にある２本のビスを回して、結像特性の良くない領域の結像特性が良好になるように、固体撮像素子５１の傾斜調整を行うとよい。
【０１５３】
このように、実施の形態３における電子スチルカメラは、偏心が存在しても、固体撮像素子を傾斜させることにより固体撮像素子の撮像面上の結像特性を良好にできるズームレンズを用いるので、撮影画像の結像特性を全領域で良好にすることができる。
【０１５４】
【発明の効果】
以上のように本発明によれば、ズーム比が２．５〜３．２倍、広角端における画角が７０°〜８０°で、解像度が高く、非使用時光学全長が短いズームレンズを提供することができる。また、本発明に係るズームレンズを用いることにより、解像度が高く、非使用時の奥行が薄い電子スチルカメラ及びビデオカメラを提供することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１に係るズームレンズの構成図
【図２】本発明の実施例１に係るズームレンズの広角端の収差図
【図３】本発明の実施例１に係るズームレンズの中間位置の収差図
【図４】本発明の実施例１に係るズームレンズの望遠端の収差図
【図５】本発明の実施例２に係るズームレンズの広角端の収差図
【図６】本発明の実施例２に係るズームレンズの中間位置の収差図
【図７】本発明の実施例２に係るズームレンズの望遠端の収差図
【図８】本発明の実施例３に係るズームレンズの広角端の収差図
【図９】本発明の実施例３に係るズームレンズの中間位置の収差図
【図１０】本発明の実施例３に係るズームレンズの望遠端の収差図
【図１１】本発明の実施例４に係るズームレンズの広角端の収差図
【図１２】本発明の実施例４に係るズームレンズの中間位置の収差図
【図１３】本発明の実施例４に係るズームレンズの望遠端の収差図
【図１４】本発明の実施例５に係るズームレンズの広角端の収差図
【図１５】本発明の実施例５に係るズームレンズの中間位置の収差図
【図１６】本発明の実施例５に係るズームレンズの望遠端の収差図
【図１７】本発明の実施の形態２に係る電子スチルカメラの概略構成図
【図１８】本発明の実施の形態３に係る電子スチルカメラの要部構成図
【符号の説明】
１０，１１ 第１レンズ群
２０，２１ 第２レンズ群
３０，３１ 第３レンズ群
２１，２２ 絞り
４０ 平行平板素子
５０ 撮像面
１ 第１レンズ
２ 第２レンズ
３ 第３レンズ
４ 第４レンズ
５ 第５レンズ
６ 第６レンズ
７ 第７レンズ
８ 第８レンズ
９ 第９レンズ
６０ ズームレンズ
５１ 固体撮像素子
６１ 液晶モニタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zoom lens, and particularly to a high-quality zoom lens used for an electronic still camera and a video camera.
[0002]
[Prior art]
2. Description of the Related Art With the progress and spread of personal computers, electronic still cameras have rapidly spread as image input devices. The total number of pixels of a solid-state imaging device used for an electronic still camera exceeds 1 million pixels, and recently, an electronic still camera equipped with a solid-state imaging device having a total number of pixels exceeding 3 million pixels has also been commercialized. In addition, video cameras have come to be equipped with a function capable of shooting high-quality still images in addition to moving images.
[0003]
The optical system of an electronic still camera includes an imaging lens, an optical low-pass filter, and a solid-state imaging device in this order from the object side. A real image corresponding to the subject is formed on the light receiving surface of the solid-state imaging device by the imaging lens. The solid-state imaging device performs spatial sampling by a pixel structure and outputs a video signal of an image formed on an imaging surface. Since the solid-state imaging device is thin, light, and small, the size of the electronic still camera can be reduced.
[0004]
A solid-state image sensor performs spatial sampling by a pixel structure. In order to remove aliasing generated in this case, an optical low-pass filter is generally arranged between an imaging lens and the solid-state image sensor to form a zoom lens. High frequency components are removed from the image. The optical low-pass filter is generally formed of a quartz plate, and utilizes the birefringence of quartz to emit an ordinary ray and an extraordinary ray separately and in parallel when natural light enters.
[0005]
In the solid-state imaging device, when the number of pixels is increased in a state where the screen size is the same, the pixel pitch decreases, so that the aperture ratio decreases and the light receiving sensitivity decreases. Therefore, a minute positive lens is provided for each pixel of the solid-state imaging device to improve the effective aperture ratio and prevent a decrease in light receiving sensitivity. In this case, in order to allow most of the light emitted from the minute positive lens to reach each corresponding pixel, the zoom lens needs to make the principal ray incident on each pixel close to parallel to the optical axis, that is, to have good telecentricity. is there.
[0006]
There are many types of electronic still cameras. One type is a compact type equipped with a zoom lens having a zoom ratio of 2 to 3 times. The compact type is required to be easy to carry, and it is necessary to shorten at least the optical overall length (the distance from the vertex of the lens surface closest to the object side of the entire lens system to the imaging surface of the solid-state imaging device) when not in use. In addition, a zoom lens having higher imaging performance and a zoom lens having a wider angle of view on the wide-angle side are required.
[0007]
As a zoom lens suitable for a compact type, the zoom lens includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and is changed by changing an interval between the two lens groups. A two-group zoom lens that performs magnification is conceivable. Such a two-unit zoom lens is characterized by being suitable for a wide angle, but has a problem that the zoom ratio is as small as about twice. In order to perform focus adjustment, it is necessary to move at least one of the two lens groups. However, since both lens groups are large and heavy, there is a problem that they are not suitable for auto focus. In order to solve this problem, many three-group zoom lenses in which a third lens group having a positive power is arranged on the image side of the two-group zoom lens have been proposed (for example, see Patent Documents 1 to 4).
[0008]
These three-unit zoom lenses are composed of, in order from the object side, a first lens unit having negative power, a second lens unit having positive power, and a third lens unit having positive power, and when zooming from the wide-angle end to the telephoto end. The air gap between the first lens group and the second lens group monotonically decreases, the air gap between the second lens group and the third lens group monotonically increases, and the third lens group is fixed or moved. Has become.
[0009]
Focus adjustment is also performed by moving the third lens group in the optical axis direction. The third lens group has an effect of improving telecentricity. Further, since the third lens group is composed of a single lens having a small outer diameter, the third lens group can be moved at high speed even with a small motor having small power, which is suitable for autofocusing. Since the movement of the first lens group and the second lens group is performed by the cylindrical cam, it is possible to use the cylindrical cam to bring all three lens groups closer to the solid-state imaging device side when not in use to form a collapsed lens. Therefore, an electronic still camera equipped with such a zoom lens can reduce the depth when not in use.
[0010]
Here, a compact electronic still camera is required to have a small depth when not in use from the viewpoint of portability, and a higher resolution of a captured image is required. To reduce the depth of the camera body when not in use, it is preferable to reduce the screen size of the solid-state imaging device and to shorten the entire optical length of the zoom lens when not in use. In order to shorten the total optical length when not in use, it is preferable to adopt the collapsible configuration as described above. Further, it is preferable to reduce the total length of each lens unit and the interval between the lens units during collapsing.
[0011]
In order to increase the resolution of a captured image, it is preferable to increase the number of pixels of the solid-state imaging device and increase the resolution of the zoom lens. However, when the screen size of the solid-state imaging device is reduced and the number of pixels is increased, it is necessary to pay attention to the fact that the image pitch of the zoom lens is deteriorated due to the influence of diffraction because the pixel pitch becomes very small. In order to reduce the influence of diffraction, it is preferable to reduce the F value of the zoom lens.
[0012]
Also, considering that an image of the peripheral portion may be cut out from the captured image, it is desired that the captured image has a more uniform resolution over the entire screen. Although the resolution uniformity of the solid-state imaging device is very good, the resolution characteristics of the zoom lens tend to be generally high at the center of the screen but low at the periphery of the screen. In addition, as the angle of view is increased, it tends to be difficult to correct distortion.
[0013]
[Patent Document 1]
JP-A-10-39214
[0014]
[Patent Document 2]
JP-A-10-307258
[0015]
[Patent Document 3]
JP 2001-42218 A
[0016]
[Patent Document 4]
JP 2001-141997 A
[0017]
[Problems to be solved by the invention]
However, the configuration of Patent Document 1 does not sufficiently correct the wide angle of view and the distortion, and the configurations of Patent Documents 2 and 3 have insufficient correction of the distortion. In this case, since the total length of each lens group is long, there has been a problem that the total optical length when not used cannot be shortened.
[0018]
In addition, the zoom lens for an electronic still camera has a problem that the processing tolerance of the lens element and the assembly tolerance of the zoom lens unit are very strict compared to the zoom lens used for a 35 mm film camera. This is because the diagonal length of the effective screen of a 35 mm film camera (36 mm horizontal × 24 mm vertical) is about 43.3 mm, whereas the diagonal length of the effective screen of a solid-state imaging device is considerably small. I have.
[0019]
In addition, the collapsible configuration requires a movable lens barrel that moves during zooming and a fixed lens barrel that holds the movable lens barrel, but if the total optical length during use is too long compared to the total optical length during collapse, However, since the fixed lens barrel cannot stably hold the movable lens barrel, there is a problem in that some lens groups are decentered, and the imaging characteristics of a captured image are deteriorated. For this reason, even if the design performance of the zoom lens is good, it is difficult to achieve an imaging performance close to the design performance in mass production because the processing tolerance and assembly tolerance of the lens element and the lens barrel part are extremely tight. There was a problem.
[0020]
The present invention has been made to solve the conventional problems as described above, and has a high resolution, a short overall optical length when not in use, a good correction of distortion, and a low eccentric sensitivity zoom lens. It is an object to provide an electronic still camera and a video camera using the same.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the zoom lens according to the present invention comprises, in order from the object side, a first lens unit having negative power, a second lens unit having positive power, a third lens unit having positive power, and a second lens unit having positive power. A zoom lens having an aperture fixed to the object side of the lens group,
The lenses constituting the first lens group are, in order from the object side, a first lens of a negative meniscus lens having a surface with a strong curvature facing the image side and a second lens of a negative meniscus lens having a surface having a strong curvature facing the image side. A second lens and a third positive lens,
The second lens group includes, in order from the object, a fourth lens of a positive lens, a fifth lens of a positive lens, a sixth lens of a negative lens, a seventh lens of a negative lens, and a positive lens. And the eighth lens of
The lens constituting the third lens group is a ninth lens of a positive lens,
Both the image side surface of the first lens and the object side surface of the fourth lens are aspheric surfaces whose local radius of curvature monotonically increases as the distance from the center increases,
The object side surface of the ninth lens is an aspheric surface,
When the shooting distance is infinity, upon zooming from the wide-angle end to the telephoto end, the first lens group draws a locus convex toward the image side, and the second lens group moves monotonously to the object side,
The zoom ratio when the shooting distance is infinity is in the range of 2.5 to 3.2 times, the angle of view at the wide-angle end is in the range of 70 ° to 80 °,
The distance from the vertex on the object side surface of the zoom lens to the image plane at the wide-angle end is represented by L_W, The distance from the vertex of the object side surface of the zoom lens at the telephoto end to the image plane is L_TF is the focal length of the entire lens system at the wide-angle end where the shooting distance is infinity._W, The focal length of the second lens group is f_G2, The focal length of the third lens group is f_G3And the focal length of the fourth lens from the object side is f₄, The focal length of the eighth lens from the object side₈Then
｜ L_W-L_T| / L_W<0.1
2.5 <f_G2/ F_W<3
5 <f_G3/ F_W<6
1.4 <f₄/ F_G2<1.6
0.5 <f₈/ F_G2<0.7
Is satisfied.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, in a three-unit zoom lens including, in order from the object side, a first lens unit having negative power, a second lens unit having positive power, and a third lens unit having positive power, a predetermined relationship is satisfied. Accordingly, a zoom lens having a high resolution and a short overall optical length when not in use can be realized.
[0023]
In the present invention, the refractive indices of the fourth lens and the fifth lens are each set to n₄, N₅And the Abbe numbers of the fourth lens and the fifth lens are respectively ν₄, Ν₅Then
n₄> 1.75
ν₄> 35
n₅> 1.6
ν₅> 45
Is preferably satisfied. According to this configuration, it is possible to reduce the axial chromatic aberration and the chromatic aberration of magnification at the time of zooming from the wide-angle end to the telephoto end, and to reduce the curvature of field.
[0024]
Further, the focal length of the first lens group is f_G1, The focal length of the first lens is f₁, The focal length of the second lens is f₂Then
0.6 <f₁/ F_G1<0.9
1.5 <f₂/ F_G1<4
Is preferably satisfied. According to this configuration, it is possible to correct the distortion generated in the first lens group and to shorten the total optical length of the first lens group.
[0025]
The radius of curvature of the object side surface of the fourth lens is r._4F, The cone constant κ_4FThe fourth order aspheric coefficient is D_4FThen
−0.9 <κ_4F+ 8D_4Fr_4F ³<-0.7
Is preferably satisfied. According to this configuration, it is possible to reduce the sensitivity of the fourth lens to the eccentricity of the object side surface with respect to the light beam having a small angle of view that passes through the central portion of the stop.
[0026]
Further, the focal length of the second lens group is f_G2And the total optical length is d_G2Then
0.7 <d_G2/ F_G2<1
Is preferably satisfied. According to this configuration, various aberrations occurring in the second lens group can be corrected in a well-balanced manner, and the total optical length of the second lens group can be shortened.
[0027]
Also, the radius of curvature of the object side surface of the first lens is r_1F, The radius of curvature of the image side_1RThe radius of curvature of the object side surface of the second lens as r_2F, The radius of curvature of the image side_2RThen
3 <r_1F/ R_1R<7
2 <r_2F/ R_2R<5
Is preferably satisfied. According to this configuration, it is easy to correct astigmatism and distortion generated in the first lens group.
[0028]
It is preferable that the fifth lens and the sixth lens are joined. According to this configuration, the overall length of the second lens group can be shortened, and the eccentric sensitivity of the second lens group can be reduced.
[0029]
Preferably, the seventh lens and the eighth lens are joined. According to this configuration, the overall length of the second lens group can be shortened, and the eccentric sensitivity of the second lens group can be reduced.
[0030]
The image side surface of the fourth lens is preferably a flat surface or a concave surface. According to this configuration, alignment is facilitated.
[0031]
Further, an electronic still camera according to the present invention includes any one of the zoom lenses and a solid-state imaging device. According to this configuration, it is possible to provide an electronic still camera having a high resolution and a small depth when not in use.
[0032]
In the above configuration, it is preferable that the solid-state imaging device is capable of adjusting a tilt. According to this configuration, the imaging characteristics of the imaging surface can be improved, and the imaging characteristics can be improved over the entire area of the captured image.
[0033]
In addition, a video camera according to the present invention includes any one of the zoom lenses and a solid-state imaging device. According to this configuration, a video camera having a high resolution and a small depth when not in use can be provided.
[0034]
(Embodiment 1)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the zoom lens according to the present embodiment, the zoom ratio when the shooting distance is infinity is in the range of 2.5 to 3.2 times, and the angle of view at the wide-angle end is in the range of 70 ° to 80 °. With this configuration, it is possible to realize a zoom lens having a high resolution, a short overall optical length when not in use, good correction of distortion, and low sensitivity to eccentricity.
[0035]
FIG. 1 is a configuration diagram of a zoom lens according to an embodiment of the present invention. FIG. 1A shows a state at a wide angle end, FIG. 1B shows a state at an intermediate position, and FIG. The state of is shown.
[0036]
The zoom lens shown in this figure includes, in order from the object side, a first lens group 10 having negative power, a second lens group 20 having positive power, and a third lens group 30 having positive power. On the image side, the optical low-pass filter 40 and the solid-state imaging device 50 are arranged in this order from the object side, and an image of the subject is formed on the imaging surface of the solid-state imaging device 50.
[0037]
The optical low-pass filter 40 includes an infrared cut filter and three quartz plates, and has a cover glass for protecting the solid-state imaging device 50. In the illustration of the optical low-pass filter 40 in FIG. 1, the infrared cut filter, the optical low-pass filter, and the cover glass are represented by one equivalent parallel plate element.
[0038]
The zoom lens according to the present embodiment is a three-unit zoom lens based on a two-unit zoom lens arranged in the order of negative power and positive power in order from the object side, and a positive-power lens group added to the image side. . The zooming of the zoom lens is performed by changing the distance between the first lens group 10 and the second lens group 20 and moving the third lens group 30 in the optical axis direction. In this case, the first lens group 10 draws a locus convex on the image side.
[0039]
The focus adjustment is performed by moving the third lens group 30 in the optical axis direction. Since the third lens group 30 is the lightest of the three lens groups, it is suitable for autofocusing in which high-speed movement of the focus adjustment lens group is desired. Further, since the third lens group 30 has an effect of improving telecentricity, it is useful when a micro lens is mounted on a solid-state imaging device.
[0040]
To reduce the total optical length of the three-unit zoom lens when not used (the distance from the vertex of the lens surface closest to the object side of the entire lens system to the imaging surface of the solid-state imaging device), the total length of the three lens units must be reduced. Good. Therefore, as will be described later, each of the three lens groups has a reduced number of components, and the overall length of each lens group is made as short as possible.
[0041]
Here, in a compact electronic still camera, it is required to reduce the overall optical length when not in use and to reduce the outer diameter of the zoom lens barrel. Since the rotation angle of the cylindrical cam has an upper limit of, for example, 120 ° or less, when the diameter of the cylindrical cam is reduced, the inclination angle of the cam groove is increased, and the first lens group 10 and the second lens group 20 are smoothly moved. Becomes difficult.
[0042]
Further, the lens barrel is composed of one fixed lens barrel and one or more movable lens barrels. In order to shorten the total optical length when retracted, it is necessary to shorten the fixed lens barrel and the movable lens barrel. However, when the ratio of the maximum value of the total optical length in use to the total optical length in the collapsed state is large, the first lens group 10 and the second lens group 20 are easily decentered with each other, and the imaging characteristics of the entire lens system are increased. Deteriorates. To solve these problems, it is effective to shorten the maximum value of the total optical length during use.
[0043]
Therefore, in the present invention, the maximum value of the optical total length in use is shortened by reducing the difference between the optical total length at the wide-angle end and the optical total length at the telephoto end, as described later. In addition, the focal length of the second lens group 20 and the focal length of the third lens group 30 are appropriately set, and the focal length of the fourth lens 4 and the focal length of the eighth lens 8 are appropriately set. The optical overall length is shortened during use after the image characteristics are improved.
[0044]
When the negative and positive two-unit zoom lens is used, the total optical length becomes the longest at the wide-angle end or the telephoto end, and becomes shortest at the middle zoom position. When a third lens group fixed at a positive power and located at the image side of the two-unit zoom lens is disposed, the third lens group is the longest at the wide-angle end or the telephoto end, and the shortest at an intermediate zoom position.
[0045]
The zoom lens according to the present invention has the following features to shorten the total length of each lens group. As shown in FIG. 1, the first lens group 10 includes, in order from the object side, a negative lens (first lens 1), a negative lens (second lens 2), and a positive lens (third lens) in order to shorten the overall length. Lens 3) is composed of three lenses. The first lens is a negative meniscus lens having a surface having a strong curvature facing the image side, the second lens is a negative meniscus lens having a surface having a strong curvature facing the image side, and the third lens is having a strong curvature. This is a positive lens whose surface faces the object side.
[0046]
Negative distortion occurs in the first lens 1 and the second lens 2 of the negative lens, but positive distortion occurs in the third lens 3 having positive power, and negative distortion at the wide-angle end of the entire lens system. Is being reduced. In order to further reduce the distortion, the first lens 1 has an aspheric surface whose local radius of curvature monotonically increases as the image side surface moves away from the center.
[0047]
The second lens group 20 includes, in order from the object side, a positive lens (fourth lens 4), a positive lens (fifth lens 5), a negative lens (sixth lens 6), a negative lens (seventh lens 7), and a positive lens (Eighth lens 8). The fourth lens 4 has a surface with a strong curvature facing the object side.
[0048]
Since the stop 21 is arranged in the vicinity of the object side of the fourth lens 4, the incident height of the axial ray becomes maximum at the fourth lens 4, and when the fourth lens 4 has a spherical surface on both sides, the fourth lens 4 does not. Generates negative spherical aberration. Therefore, the spherical aberration generated in the third lens group 30 is reduced as an aspheric surface in which the local radius of curvature monotonically increases as the object side surface of the fourth lens 4 moves away from the center.
[0049]
Also, the fifth lens 5 and the sixth lens 6 are joined, and the seventh lens 7 and the eighth lens 8 are joined, so that the entire length of the second lens group 20 is shortened.
[0050]
Since the third lens group 30 is composed of one positive lens (the ninth lens 9), its total length is short. The ninth lens 9 generates a positive distortion with the object side surface being an aspheric surface, so that the absolute value of the negative distortion at the wide-angle end is reduced. In the example of FIG. 1, the ninth lens 9 is a convex meniscus lens, but may be a biconvex lens.
[0051]
Focus adjustment is performed by moving only the third lens group 30 in the optical axis direction without moving the first lens group 10 and the second lens group 20. As the photographing distance becomes shorter, the third lens group 30 moves toward the object side. The third lens group 30 is composed of one lens, and the moving part including other moving mechanical parts is light, so that even a small motor with small power can be moved at high speed, and the auto focus adjustment can be performed. It can be performed at high speed. Although the chromatic aberration of magnification changes when the ninth lens 9 moves for the purpose of focus adjustment, the chromatic aberration of magnification is suppressed to such an extent that there is no practical problem.
[0052]
Hereinafter, the present embodiment will be described more specifically using conditional expressions. In the following conditional expression, L_WIs the total optical length at the wide-angle end, L_TIs the total optical length at the telephoto end, f_WIs the focal length at the wide angle end of the entire lens system. f_GiIs the focal length of the ith (i is an integer) lens group as viewed from the object side.
[0053]
When the i-th lens (i is an integer) as viewed from the object side is the i-th lens, f_iIs the focal length of the i-th lens, n_iIs the refractive index of the i-th lens, ν_iIs the Abbe number of the i-th lens, r_iFIs the radius of curvature of the object side surface of the i-th lens, r_iRIs the radius of curvature of the image side surface of the i-th lens, and κ_4FIs the conic constant, D_4FIs the fourth order aspheric coefficient, d_G2Is the total optical length of the second lens group.
[0054]
The zoom lens according to the present embodiment satisfies the following conditional expressions (1) to (5).
[0055]
Formula (1) | L_W-L_T| / L_W<0.1
Formula (2) 2.5 <f_G2/ F_W<3
Equation (3) 5.0 <f_G3/ F_W<6
Equation (4) 1.4 <f₄/ F_G2<1.6
Equation (5) 0.5 <f₈/ F_G2<0.7
Conditional expression (1) represents a condition for shortening the maximum value of the total optical length during use and ensuring good imaging characteristics. In order to shorten the maximum value of the total optical length at the time of use, it is ideal that the total optical length at the wide-angle end is equal to the total optical length at the telephoto end. However, if the total optical length at the wide-angle end and the total optical length at the telephoto end are to be made completely equal, the imaging characteristics may be sacrificed in some cases. Conditional expression (1) is a condition obtained in consideration of this. If conditional expression (1) is not satisfied, it becomes difficult to shorten the total optical length during use and to ensure good imaging characteristics.
[0056]
Conditional expression (2) represents conditions for shortening the total optical length during use as much as possible and for correcting the occurrence of various aberrations in a well-balanced manner. f_G2/ F_WExceeds the upper limit, the distance between the object and the image of the second lens group becomes long, so that the total optical length in use becomes long. In this case, if the magnification of the third lens group is reduced, the total optical length is shortened, but the power of the third lens group is increased. Is difficult to correct by the first lens group and the second lens group.
[0057]
On the other hand, f_G2/ F_WIs less than the lower limit, the overall optical length becomes short in use, but it is difficult to secure an air gap at the telephoto end between the first lens unit and the second lens unit so that a stop can be arranged.
[0058]
Conditional expression (3) represents a condition for reducing the inclination angle of the principal ray at the maximum image height incident on the solid-state imaging device, that is, improving the telecentricity and reducing the field curvature. f_G3/ F_WExceeds the lower limit, the telecentricity is improved, but the field curvature of the entire lens system cannot be corrected.
[0059]
On the other hand, f_G3/ F_WExceeds the upper limit, the field curvature is reduced, but the telecentricity becomes insufficient.
[0060]
Conditional expressions (4) and (5) represent conditions for correcting various aberrations occurring in the second lens group in a well-balanced manner, and for shortening the total optical length of the entire lens system during use. f₄/ F_G2Exceeds the upper limit, or f₈/ F_G2Is less than the lower limit, the deviation of the object-side principal point of the second lens unit toward the object side is insufficient. Therefore, if the distance from the image-side principal point of the first lens group to the object-side principal point of the second lens group is set to a desired length at the telephoto end, the distance between the first and second lens groups is reduced. It becomes impossible to secure a space in which the aperture can be arranged.
[0061]
On the other hand, f₄/ F_G2Exceeds the lower limit, or f₈/ F_G2Exceeds the upper limit, the bias of the object side principal point of the second lens group G2 toward the object side is sufficient. For this reason, at the telephoto end, a space for arranging the stop between the first lens group and the second lens group can be secured, and the total optical length during use can be shortened. However, since the power of the fifth lens becomes excessive, it becomes difficult to correct spherical aberration and coma generated by the fifth lens with good balance by other lenses.
[0062]
Further, it is preferable to satisfy the following conditional expressions (6) to (9).
[0063]
Equation (6) n₄> 1.75
Equation (7) ν₄> 35
Equation (8) n₅> 1.6
Equation (9) ν₅> 45
The conditional expressions (6) to (9) represent conditions for reducing the axial chromatic aberration and the chromatic aberration of magnification upon zooming from the wide-angle end to the telephoto end, and for reducing the field curvature. If any one of the conditional expressions (6) to (9) is not satisfied, the axial chromatic aberration or the chromatic aberration of magnification increases at any zoom position, so that color blur does not stand out or the field curvature does not decrease. There is a problem that the imaging characteristics are not good in a part of the captured image.
[0064]
Further, it is preferable to satisfy the following conditional expressions (10) to (11).
[0065]
Equation (10) 0.6 <f₁/ F_G1<0.9
Equation (11) 1.5 <f₂/ F_G1<4
Conditional expressions (10) and (11) represent conditions for correcting the distortion generated in the first lens group and shortening the total optical length of the first lens group. f₁/ F_G1Or f₂/ F_G1Exceeds the upper limit, it becomes easy to correct distortion, but the total optical length of the first lens group becomes long. For this reason, the total optical length when used and the total optical length when retracted are increased.
[0066]
On the other hand, f₁/ F_G1Or f₂/ F_G1Exceeds the lower limit, the total optical length of the first lens group can be shortened, but it becomes difficult to correct distortion.
[0067]
Further, it is preferable that the following conditional expression (12) is satisfied.
[0068]
Equation (12) −0.9 <κ_4F+ 8D_4Fr_4F ³<-0.7
Conditional expression (12) satisfies the condition that the conical constant relating to the aspherical surface on the object side surface of the fourth lens and the fourth-order aspherical surface coefficient are restricted, so that the light beam passing through the central portion of the stop and having a small angle of view is converted into the fourth lens. This represents a condition for reducing the eccentric sensitivity of the object side surface of the lens. κ_4F+ 8D_4Fr_4F ³Represents the degree of deviation of the aspherical surface from the spherical surface. κ_4F+ 8D_4Fr_4F ³Is less than the lower limit, the spherical aberration generated on the object side of the fourth lens decreases due to the effect of the aspherical surface, but the eccentric coma and the eccentric astigmatism generated on the object side of the fourth lens become excessive. The sensitivity of the fourth lens to the eccentricity of the object side surface increases.
[0069]
On the other hand, κ_4F+ 8D_4Fr_4F ³Exceeds the upper limit, the eccentric coma aberration and the eccentric astigmatism generated on the object side of the fourth lens are reduced, but the spherical aberration is insufficiently corrected.
[0070]
Further, it is preferable that the following conditional expression (13) is satisfied.
[0071]
Equation (13) 0.7 <d_G2/ F_G2<1
Conditional expression (13) represents conditions for correcting various aberrations generated in the second lens group in a well-balanced manner, and shortening the total optical length of the second lens group. d_G2/ F_G2Exceeds the upper limit, the total optical length of the second lens group G2 cannot be shortened. On the other hand, d_G2/ F_G2  Exceeds the lower limit, it becomes difficult to correct spherical aberration and coma in a well-balanced manner.
[0072]
Further, it is preferable to satisfy the following conditional expressions (14) and (15).
[0073]
Equation (14) 3 <r_1F/ R_1R<7
Equation (15) 2 <r_2F/ R_2R<5
Conditional expressions (14) and (15) represent conditions for correcting astigmatism and distortion generated in the first lens group. When the value exceeds the upper limit, distortion is easily corrected, but astigmatism is insufficiently corrected. On the other hand, if the lower limit is exceeded, it becomes difficult to correct the distortion.
[0074]
Hereinafter, examples of the present embodiment will be described. The basic configuration of the zoom lens according to each of the following examples is the same as that shown in FIG.
[0075]
(Example 1)
The zoom lens according to the first embodiment has a collapsible configuration in which the first lens group 10, the second lens group 20, and the third lens group 30 are moved toward the solid-state imaging device 50 when not in use. ing. The collapsible configuration can be realized by extending the cam groove of the cylindrical cam that moves the first lens group 10 and the second lens group 20 in the optical axis direction.
[0076]
A part of the lens of Example 1 is aspherical, and the aspherical shape is defined by the following (Equation 1). The description regarding the aspherical surface and the intermediate position between the zoom positions described using (Equation 1) to (Equation 3) is the same for the following Examples 2 to 5.
[0077]
(Equation 1)

[0078]
Here, κ is a conical constant, r is the radius of curvature of the aspherical vertex, D, E, F, and G are the fourth-, sixth-, eighth-, and tenth-order aspherical coefficients, respectively, and h is the height from the optical axis. , Z is the sag amount at a point where the height from the optical axis on the aspheric surface is h.
[0079]
The local radius of curvature ρ at a point where the height of the aspheric surface from the optical axis is h is given by the following (Equation 2).
[0080]
(Equation 2)

[0081]
The focal length at the wide-angle end when the shooting distance is infinity is f_WAnd the focal length at the telephoto end is f_TThen, the following (Equation 3) focal length f_NIs referred to as an intermediate position.
[0082]
(Equation 3)

[0083]
Table 1 below shows the lens data of the zoom lens.
[0084]
[Table 1]

[0085]
The aspheric surface data is shown in Table 2 below.
[0086]
[Table 2]

[0087]
Table 3 below shows variable surface interval data when the shooting distance is infinity.
[0088]
[Table 3]

[0089]
The units of length in the table are all mm. r is the radius of curvature, d is the surface spacing, nd and νd are the refractive index and Abbe number at the d-line, respectively. G1 to G3 correspond to the first to third lens groups, L1 to L9 correspond to the first to ninth lenses, and P corresponds to the parallel plate element 40. The surfaces marked with * are aspherical surfaces. In Table 3, d6, d17, and d19 are surface intervals of the variable portion, and the positions are shown in FIG. 1, where f is the focal length, F is the F number, ω (°) is the half angle of incidence, L indicates the total optical length. The description about these tables is the same in each of the following tables.
[0090]
FIGS. 2 to 4 show aberration diagrams of the zoom lens according to the first embodiment when the shooting distance is infinity and the aperture is fully opened. 2 shows the case at the wide-angle end, FIG. 3 shows the case at the intermediate position, and FIG. 4 shows the case at the telephoto end. In each figure, (a) shows spherical aberration (mm), (b) shows astigmatism (mm), and (c) shows distortion (%).
[0091]
In the spherical aberration diagram, the solid line indicates the characteristics of the d-line, the short dashed line indicates the characteristics of the F-line, and the long dashed line indicates the characteristics of the C-line. In the astigmatism diagram, the solid line shows the characteristics of the sagittal plane, and the broken line shows the characteristics of the meridional plane. From FIG. 2 to FIG. 4, it can be seen that various aberrations are satisfactorily corrected even when the zoom position changes.
[0092]
In the first embodiment, as the solid-state imaging device, a device having an effective pixel number of 2048 horizontal × 1536 vertical, a pixel pitch of 2.8 μm horizontal × 2.8 μm vertical, and an effective screen size of 5.7344 mm horizontal × 4.3008 mm vertical is used. be able to. Further, as the solid-state imaging device, a device provided with a microlens for each pixel for improving the effective aperture ratio can be used. This is the same for the following Examples 2 to 5.
[0093]
In the zoom lens shown in FIG. 1, the sensitivity of the second lens group to eccentricity is high. Therefore, in the configuration of FIG. 1, the fifth lens 5 and the sixth lens 6 are joined, and the seventh lens 7 and the eighth lens 8 are joined. The fourth lens 4 has a concave image side surface so that the fourth lens 4 can be easily aligned at the time of assembly if necessary.
[0094]
When the fifth lens 5 and the sixth lens 6 and the seventh lens 7 and the eighth lens 8 are joined, the difference in the refractive index at the boundary between the two surfaces of the adhesive becomes small, so that the eccentric sensitivity becomes low. Further, in the case of joining, since a spacer that easily causes a surface gap error is not required, the error of the surface space can be reduced as compared with the case where the spacer is used.
[0095]
When performing centering, the following should be performed. After assembling the lens in which the fifth lens 5 and the sixth lens 6 are joined and the lens in which the seventh lens 7 and the eighth lens 8 are joined into a lens frame, the fourth lens 4 is attached to a predetermined position, and is decentered. The position of the fourth lens 4 is adjusted so as to reduce the eccentricity of the entire second lens group 20 using a measuring device, and finally the fourth lens 4 is fixed to the lens frame with an adhesive.
[0096]
At this time, when the image side surface of the fourth lens 4 is a convex surface, when the fourth lens 4 is moved, both parallel eccentricity and inclined eccentricity are generated, so that alignment becomes difficult. On the other hand, as described above, if the image side surface of the fourth lens 4 is concave (or flat), the fourth lens 4 can be moved in parallel without being tilted, so that centering is facilitated. .
[0097]
Further, by inclining the solid-state imaging device within 1 °, it is possible to improve the imaging characteristics on the solid-state imaging device.
[0098]
As described above, the zoom lens according to Example 1 has a zoom ratio of 3.0 times, an angle of view at the wide-angle end of about 76.5 °, a high resolution, a short overall optical length when not in use, and low distortion. It has been corrected well.
[0099]
Note that the description regarding the above-described joining of the lenses, alignment, and inclination of the solid-state imaging device is the same for the following Examples 2 to 5.
[0100]
(Example 2)
The basic configuration of the zoom lens according to the second embodiment is the same as that of the first embodiment, but the second embodiment differs from the first embodiment in the material of some lenses. Table 4 below shows lens data of the zoom lens according to Example 2.
[0101]
[Table 4]

[0102]
The aspheric surface data is shown in Table 5 below.
[0103]
[Table 5]

[0104]
Table 6 below shows variable surface interval data when the shooting distance is infinity.
[0105]
[Table 6]

[0106]
FIGS. 5 to 7 show aberration diagrams of the zoom lens according to the second embodiment when the shooting distance is infinity and the aperture is fully opened. It can be seen from FIGS. 5 to 7 that various aberrations are well corrected even when the zoom position changes.
[0107]
Also in the present embodiment, since the image surface side of the fourth lens is concave, if necessary, the alignment of the fourth lens can be easily performed similarly to the first embodiment. Further, by inclining the solid-state imaging device within 1 °, it is possible to improve the imaging characteristics on the solid-state imaging device.
[0108]
As described above, the zoom lens according to Example 2 has a zoom ratio of 3.0 times, an angle of view at the wide-angle end of about 76.5 °, a high resolution, a short overall optical length when not in use, and low distortion. It has been corrected well.
[0109]
(Example 3)
The basic configuration of the zoom lens according to the third embodiment is the same as that of the first embodiment, but the third embodiment differs from the third embodiment in the material of some lenses. Table 7 below shows lens data of the zoom lens according to Example 3.
[0110]
[Table 7]

[0111]
The aspheric surface data is shown in Table 8 below.
[0112]
[Table 8]

[0113]
Table 9 below shows variable surface interval data when the shooting distance is infinity.
[0114]
[Table 9]

[0115]
8 to 10 show aberration diagrams of the zoom lens according to the third embodiment when the shooting distance is infinity and the aperture is fully opened. 8 to 10, it can be seen that various aberrations are favorably corrected even when the zoom position changes.
[0116]
Also in the present embodiment, since the image surface side of the fourth lens is concave, if necessary, the alignment of the fourth lens can be easily performed similarly to the first embodiment. Further, by inclining the solid-state imaging device within 1 °, it is possible to improve the imaging characteristics on the solid-state imaging device.
[0117]
As described above, the zoom lens according to Example 3 has a zoom ratio of 3.0 times, an angle of view at the wide-angle end of about 76.5 °, a high resolution, a short overall optical length when not in use, and low distortion. It has been corrected well.
[0118]
(Example 4)
The basic configuration of the zoom lens according to the fourth embodiment is the same as that of the first embodiment, but the fourth embodiment differs from the first embodiment in the material of some lenses. Table 10 below shows lens data of the zoom lens according to Example 4.
[0119]
[Table 10]

[0120]
The aspheric surface data is shown in Table 11 below.
[0121]
[Table 11]

[0122]
Table 12 below shows variable surface interval data when the shooting distance is infinity.
[0123]
[Table 12]

[0124]
FIGS. 11 to 13 show aberration diagrams when the shooting distance of the zoom lens according to the fourth embodiment is infinity and the aperture is fully opened. It can be seen from FIGS. 11 to 13 that various aberrations are favorably corrected even when the zoom position changes.
[0125]
Also in the present embodiment, since the image surface side of the fourth lens is concave, if necessary, the alignment of the fourth lens can be easily performed similarly to the first embodiment. Further, by inclining the solid-state imaging device within 1 °, it is possible to improve the imaging characteristics on the solid-state imaging device.
[0126]
As described above, the zoom lens according to Example 4 has a zoom ratio of 3.0 times, an angle of view at the wide angle end of about 76.5 °, a high resolution, a short overall optical length when not in use, and a low distortion. It has been corrected well.
[0127]
(Example 5)
The basic configuration of the zoom lens according to the fifth embodiment is the same as that of the first embodiment, but the fourth embodiment differs from the fourth embodiment in the material of some lenses. Table 13 below shows lens data of the zoom lens according to Example 5.
[0128]
[Table 13]

[0129]
The aspherical data is shown in Table 14 below.
[0130]
[Table 14]

[0131]
Table 15 below shows the variable surface interval data when the shooting distance is infinity.
[0132]
[Table 15]

[0133]
14 to 16 show aberration diagrams of the zoom lens according to Example 5 when the shooting distance is infinity and the aperture is fully opened. It can be seen from FIGS. 14 to 16 that various aberrations are favorably corrected even when the zoom position changes.
[0134]
Also in the present embodiment, since the image surface side of the fourth lens is concave, if necessary, the alignment of the fourth lens can be easily performed similarly to the first embodiment. Further, by inclining the solid-state imaging device within 1 °, it is possible to improve the imaging characteristics on the solid-state imaging device.
[0135]
As described above, the zoom lens according to Example 5 has a zoom ratio of 3.0 times, an angle of view at the wide-angle end of about 76.5 °, a high resolution, a short overall optical length when not in use, and low distortion. It has been corrected well.
[0136]
Table 16 shows values of the conditional expressions (1) to (15) of Examples 1 to 5. In Table 16, E-04 is represented by × 10.^-4That is.
[0137]
[Table 16]

[0138]
(Embodiment 2)
FIG. 17 is a schematic configuration diagram of an electronic still camera according to Embodiment 2 of the present invention. In FIG. 17, reference numeral 60 denotes a zoom lens, 51 denotes a solid-state image sensor, 61 denotes a liquid crystal monitor, 11 denotes a first lens group, 22 denotes an aperture, 21 denotes a second lens group, and 31 denotes a third lens group.
[0139]
The zoom lens 60 is arranged on the front side of the housing 62, and the optical low-pass filter 41 and the solid-state imaging device 51 are arranged on the rear side of the zoom lens 60 in order from the object side. A liquid crystal monitor 61 is arranged on the rear side of the housing 62, and the solid-state imaging device 51 and the liquid crystal monitor 61 are close to each other.
[0140]
The optical low-pass filter 41 is formed by joining a first quartz plate, a second quartz plate, and a third quartz plate with a transparent adhesive in order from the object side. The three quartz plates are parallel planes, and each optical axis is inclined by 45 ° with respect to the optical axis. The direction in which the optical axis of each crystal plate is projected on the imaging surface 52 of the solid-state imaging device 51 is, as viewed from the zoom lens 60 side, the direction in which the first crystal plate is rotated 45 ° counterclockwise from the screen horizontal direction, The second crystal plate is in a direction rotated 45 ° clockwise from the horizontal direction of the screen, and the third crystal plate is in the horizontal direction of the screen. The optical low-pass filter 41 prevents generation of an erroneous signal such as moire caused by the pixel structure of the solid-state imaging device 51. On the object side surface of the optical low-pass filter 41, an optical multilayer film that reflects infrared light and transmits visible light is deposited.
[0141]
The solid-state imaging device 51 has an effective number of pixels of 2048 × 1536, a pixel pitch of 2.8 μm × 2.8 μm, and an effective screen size of 5.7344 mm × 4.3008 mm. A lens is provided. A cover glass 42 is provided on the object side of the solid-state imaging device 51. An image of the subject by the zoom lens 60 is formed on the imaging surface 52.
[0142]
As the zoom lens 60, the zoom lens shown in FIG. 1 is used. The zoom lens 60 includes a first lens group 11, a stop 22, a second lens group 21, and a third lens group 31 in this order from the object side.
[0143]
The lens barrel includes a movable lens barrel 63, a first cylindrical cam 64, a main lens barrel 65, a second cylindrical cam 66, a second lens group frame 67, and a third lens group frame 68. The first lens group 11 is mounted on a movable lens barrel 63, the second lens group 21 and the stop 22 are mounted on a second lens group frame 67, and the third lens group 31 is mounted on a third lens group frame 68. I have. When the second cylindrical cam 66 is rotated, the first cylindrical cam 64 is moved in the optical axis direction while rotating, and when the first cylindrical cam 64 is rotated, the movable lens barrel 63 and the second lens group frame 67 are moved. It is designed to move. When the second cylindrical cam 66 is rotated in this manner, the first lens group 11 and the second lens group 21 move to predetermined positions based on the solid-state imaging device 51, and change from the wide-angle end to the telephoto end. You can do double.
[0144]
The third lens group frame 68 is movable in the optical axis direction by a focus adjustment motor. When the third lens group 31 is moved in the direction of the optical axis by the motor, the position where the high frequency component of the photographed image becomes a peak is detected, and if the third lens group 31 is moved to that position, the autofocus adjustment is performed. Can be.
[0145]
If the first lens group 11, the second lens group 21, and the third lens group 31 are all moved toward the solid-state imaging device 51 side when not in use, it becomes a retractable type, and the total optical length of the zoom lens when not in use is very short. be able to. The first lens group 11 and the second lens group 21 can be moved toward the solid-state imaging device 51 by extending the cam grooves of the first cylindrical cam 64 and the second cylindrical cam 66.
[0146]
Thus, it is possible to provide an electronic still camera having a zoom ratio of 2.5 to 3.2 times, an angle of view at the wide-angle end of about 70 ° to 80 °, a high resolution, and a small depth when not in use.
[0147]
Note that any of the zoom lenses described in the first to fifth embodiments may be used as the zoom lens of the electronic still camera shown in FIG.
[0148]
The optical system of the electronic still camera shown in FIG. 17 can be used for a video camera for moving images. In this case, not only a high-resolution still image but also a moving image can be captured.
[0149]
(Embodiment 3)
FIG. 18 shows a waist configuration diagram of the electronic still camera according to the third embodiment. Components having the same configuration as in FIG. 17 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 18 shows a configuration in which the solid-state imaging device 51 is attached to the zoom lens 60 with an inclination in the electronic still camera as shown in FIG.
[0150]
The mounting plate 70 is mounted on the solid-state imaging device 51. The mounting plate 70 is provided with holes at three peripheral portions, and the main lens barrel 65 is provided with screw holes at three positions corresponding to the three holes of the mounting plate 70. Two holes are provided near two of the three screw holes of the main lens barrel 65, and a spring 72 is inserted into each of the two holes. The mounting plate 70 is attached to the main barrel 65, and three screws 71 (one screw is not shown) are attached to the main barrel through three holes of the mounting plate 70. At this time, since the spring 72 acts to press the mounting plate 70, the inclination angle and the inclination direction of the solid-state imaging device 51 can be freely changed by turning the screw 71 near the spring 72. If the three screws are fixed with an adhesive after the adjustment is completed, the position and orientation of the solid-state imaging device 51 with respect to the zoom lens 60 can be stably maintained thereafter.
[0151]
In this way, when each lens surface of the zoom lens 60 is eccentric, when the solid-state imaging device 51 is attached so that the imaging surface 52 is perpendicular to the optical axis of the zoom lens 60, a part of the imaging surface 52 In some cases, the imaging characteristics are not good in the region, but by appropriately tilting the solid-state imaging device 51, the imaging characteristics of the region in which the imaging characteristics are poor on the imaging surface 52 can be improved.
[0152]
The inclination angle range of the solid-state imaging device 51 is preferably set to about 1 °. The tilt adjustment of the solid-state imaging device 51 is performed by actually shooting at several zoom positions from the wide-angle end to the telephoto end, searching for an area having poor imaging characteristics from the output signal from the solid-state imaging device 51, and then outputting the image. While observing the signal, the two screws near the two springs 72 may be turned to adjust the tilt of the solid-state imaging device 51 so that the image forming characteristics in the area where the image forming characteristics are not good are improved. .
[0153]
As described above, the electronic still camera according to Embodiment 3 uses the zoom lens that can improve the imaging characteristics on the imaging surface of the solid-state imaging device by inclining the solid-state imaging device even when eccentricity exists. The imaging characteristics of the captured image can be improved in all regions.
[0154]
【The invention's effect】
As described above, according to the present invention, there is provided a zoom lens having a zoom ratio of 2.5 to 3.2 times, an angle of view at the wide angle end of 70 ° to 80 °, a high resolution, and a short overall optical length when not in use. can do. Further, by using the zoom lens according to the present invention, an electronic still camera and a video camera having a high resolution and a small depth when not in use can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a zoom lens according to Embodiment 1 of the present invention;
FIG. 2 is an aberration diagram at a wide-angle end of a zoom lens according to Embodiment 1 of the present invention.
FIG. 3 is an aberration diagram at an intermediate position of the zoom lens according to the first embodiment of the present invention.
FIG. 4 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 1 of the present invention;
FIG. 5 is an aberration diagram at a wide-angle end of a zoom lens according to a second embodiment of the present invention.
FIG. 6 is an aberration diagram at an intermediate position of the zoom lens according to Embodiment 2 of the present invention;
FIG. 7 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 2 of the present invention;
FIG. 8 is an aberration diagram at a wide-angle end of a zoom lens according to Embodiment 3 of the present invention;
FIG. 9 is an aberration diagram at an intermediate position of the zoom lens according to Embodiment 3 of the present invention.
FIG. 10 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 3 of the present invention;
FIG. 11 is an aberration diagram at a wide-angle end of a zoom lens according to Embodiment 4 of the present invention;
FIG. 12 is an aberration diagram at an intermediate position of the zoom lens according to Embodiment 4 of the present invention;
FIG. 13 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 4 of the present invention;
FIG. 14 is an aberration diagram at a wide-angle end of a zoom lens according to Embodiment 5 of the present invention.
FIG. 15 is an aberration diagram at an intermediate position of the zoom lens according to Embodiment 5 of the present invention.
FIG. 16 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 5 of the present invention;
FIG. 17 is a schematic configuration diagram of an electronic still camera according to Embodiment 2 of the present invention.
FIG. 18 is a main part configuration diagram of an electronic still camera according to Embodiment 3 of the present invention.
[Explanation of symbols]
10, 11 First lens group
20, 21 Second lens group
30, 31 Third lens group
21, 22 aperture
40 parallel plate element
50 Imaging surface
1 First lens
2 Second lens
3 Third lens
4 Fourth lens
5 Fifth lens
6 sixth lens
7 Seventh lens
8 8th lens
9 Ninth lens
60 zoom lens
51 Solid-state image sensor
61 LCD monitor

Claims (12)

A zoom lens including, in order from the object side, a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, and a diaphragm fixed to the object side of the second lens group. A lens,
The lenses constituting the first lens group are, in order from the object side, a first lens of a negative meniscus lens having a surface with a strong curvature facing the image side and a second lens of a negative meniscus lens having a surface with a strong curvature facing the image side. A second lens and a third positive lens,
The second lens group includes, in order from the object, a fourth lens of a positive lens, a fifth lens of a positive lens, a sixth lens of a negative lens, a seventh lens of a negative lens, and a positive lens. And the eighth lens of
The lens constituting the third lens group is a ninth lens of a positive lens,
Both the image side surface of the first lens and the object side surface of the fourth lens are aspheric surfaces whose local radius of curvature monotonically increases as the distance from the center increases,
The object side surface of the ninth lens is an aspheric surface,
When the shooting distance is infinity, upon zooming from the wide-angle end to the telephoto end, the first lens group draws a locus convex toward the image side, and the second lens group moves monotonously to the object side,
The zoom ratio when the shooting distance is infinity is in the range of 2.5 to 3.2 times, the angle of view at the wide angle end is in the range of 70 ° to 80 °,
The distance from the vertex of the object side surface of the zoom lens to the image plane at the wide angle end is L _W , the distance from the vertex of the object side surface of the zoom lens at the telephoto end to the image plane is L _T , and the shooting distance is infinity and wide angle. The focal length of the entire lens system at the end is f _W , the focal length of the second lens group is f _G2 , the focal length of the third lens group is f _G3 , and the focal length of the fourth lens from the object side is f _4. If the focal length of the _eighth lens from the object side is f8,
_{| L W -L T | / L} W <0.1
2.5 <f _G2 / f _W <3
5 <f _G3 / f _W <6
1.4 <f ₄ / f _G2 <1.6
0.5 <f ₈ / f _G2 <0.7
A zoom lens that satisfies the following relationship. Assuming that the refractive indices of the fourth lens and the fifth lens are n ₄ and n _5, and the Abbe numbers of the fourth lens and the fifth lens are ν ₄ and ν ₅ respectively,
n ₄ > 1.75
ν ₄ > 35
n ₅ > 1.6
ν ₅ > 45
The zoom lens according to claim 1, wherein the following relationship is satisfied. Assuming that the focal length of the first lens group is f _G1 , the focal length of the first lens is f ₁ , and the focal length of the second lens is f ₂ ,
0.6 <f ₁ / f _G1 <0.9
1.5 <f ₂ / f _G1 <4
3. The zoom lens according to claim 1, wherein the following relationship is satisfied. When the radius of curvature of the object side surface of the fourth lens is r _4F , the conic constant is κ _4F , and the fourth-order aspheric coefficient is D _4F ,
−0.9 <κ _4F + 8D _4F r _4F ³ <−0.7
4. The zoom lens according to claim 1, wherein the following relationship is satisfied. If the focal length of the second lens group is f _G2 and the total optical length is d _G2 ,
0.7 < _dG2 / _fG2 <1
The zoom lens according to any one of claims 1 to 4, wherein the following relationship is satisfied. When the radius of curvature of the object side surface of the first lens is r _1F , the radius of curvature of the image side surface is r _1R , the radius of curvature of the object side surface of the second lens is r _2F , and the radius of curvature of the image side surface is r _2R ,
3 <r _1F / r _1R <7
2 <r _2F / r _2R <5
The zoom lens according to any one of claims 1 to 5, wherein the following relationship is satisfied. The zoom lens according to claim 1, wherein the fifth lens and the sixth lens are cemented. The zoom lens according to any one of claims 1 to 7, wherein the seventh lens and the eighth lens are cemented. The zoom lens according to claim 1, wherein an image side surface of the fourth lens is a flat surface or a concave surface. An electronic still camera comprising the zoom lens according to claim 1 and a solid-state imaging device. The electronic still camera according to claim 10, wherein an inclination of the solid-state imaging device is adjustable. A video camera comprising the zoom lens according to claim 1 and a solid-state imaging device.

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